Techniques for On-Demand Production of Medical Radioactive Iodine Isotopes Including I-131

Abstract

A system for radioisotope production uses fast-neutron-caused fission of depleted or naturally occurring uranium targets in an irradiation chamber. Fast fission can be enhanced by having neutrons encountering the target undergo scattering or reflection to increase each neutron's probability of causing fission (n, f) reactions in U-238. The U-238 can be deployed as one or more layers sandwiched between layers of neutron-reflecting material, or as rods surrounded by neutron-reflecting material. The gaseous fission products can be withdrawn from the irradiation chamber on a continuous basis, and the radioactive iodine isotopes (including I-131) extracted.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS[0001]This application claims priority to the following U.S. patent applications:[0002]U.S. Provisional Patent Application No. 61 / 260,585 filed Nov. 12, 2009 for “Medical Isotope Production on Demand”;[0003]U.S. Provisional Patent Application No. 61 / 265,383 filed Dec. 1, 2009 for “System for On-Demand Production of I-131”;[0004]U.S. Provisional Patent Application No. 61 / 405,605 filed Oct. 21, 2010 for “Techniques for On-Demand Production of Medical Isotopes Such as Mo-99 / Tc-99m.”[0005]This application is also related to U.S. patent application Ser. No. 12 / 944,634 filed contemporaneously herewith for “Techniques for On-Demand Production of Medical Isotopes Such As Mo-99 / Tc-99m and Radioactive Iodine Isotopes Including I-131” (inventor Francis Yu-Hei Tsang).[0006]The entire disclosures of all the above mentioned applications, including all appendices and attachments, are hereby incorporated by reference for all purposes.BACKGROUND OF THE INVENTI...

AI Technical Summary

Benefits of technology

[0022]Embodiments of the present invention provide techniques for the production of radioactive iodine isotopes. Radioisotopes that are useful in the field of medicine are sometimes referred to as medical isotopes, although some stable isotopes have potential medical uses and are sometimes referred to as stable medical isotopes. The techniques provided by the invention overcome at least some of the problems discussed above. Embodiments do not rely on a nuclear reactor far from the delivery site, but can be implemented as relatively small stand-alone devices that can be widely distributed.

[0045]In some embodiments, the method further includes allowing a period of time to elapse so that at least one short-lived radioactive iodine isotope substantially decays to a non-iodine substance; and separating the non-iodine substance from the remaining radioactive iodine.

[0053]Embodiments of the present invention operate to enhance fast fission in NEU targets by having neutrons undergo scattering or reflection after passing through a region of NEU. This is accomplished by having the target material interspersed with what is referred to as “neutron-reflecting” material, which reflects or scatters neutrons so that the neutrons travel a longer path before leaving the target material. This provides more opportunities for the neutrons to cause fission reactions with the NEU target material.

[0057]In one set of embodiments, the NEU and neutron-reflecting material are formed as alternating layers of NEU and neutron-reflecting material. The layers can take the form of spherical shells, cylindrical shells, flat plates and the like, with a fast neutron generator disposed near the center. In these embodiments, the irradiation chamber is generally spherical, generally cylindrical, or generally rectangular. Other geometries such as polygonal cylinders and polyhedrons are also possible, and may allow easier fabrication.

Problems solved by technology

A major obstacle to a reliable source is the fact that 100% of the U.S. supply is imported from foreign reactors.

The rapid decay of the Mo-99 means that product must be shipped and used immediately with no long term storage possible.

Any interruptions in supply, even brief periods such as a reactor shutting down for maintenance, can cause shortages and patient treatment delays.

When a thyroid gland is overactive, it produces too much of these thyroid hormones, accelerating the metabolism.

The spent HEU target material is also a threat because only between 1-3% of the U-235 in the HEU target is burned up and the remaining target material can still contain 92% enriched U-235.

Alternative techniques have been proposed, but they are thought to be significantly less cost effective and many technical challenges remain.

One such proposal is to transition to a lower level of enrichment of the U-235 target (LEU), say below 20% U-235, but this still presents the same problems as HEU, including the need for a nuclear reactor.

The proposed alternative methods using particle accelerators all have similar problems:They all require large and enriched isotopic targets.They all require heat removal from the targets during irradiation, which represents a technical challenge.The Mo-99 produced must be purified to remove unused molybdenum isotopes and other fission products and activation by-products.They all require development of fast dissolution methods for the metallic targets.Treatment and disposal of the waste fission products and waste uranium present significant challenges (for LEU).

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